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The Transgenic Tomato
Overview The transgenic tomato is a genetically modified version of the tomato. Genetically-modifying tomatoes increases the tomatoes shelf-life, increases the resistance to pests and increases the resistance to environmental stress. Genetically-modifying tomatoes started in the 1980s. Wild-type tomatoes started out very small, green and extremely bitter. They have been artificially bred for many centuries, with the hopes of increasing the size and making them sweeter (2). Agrobacerium tumefaciens Agrobacerium tumefaciens is a soil dwelling bacteria that has the ability to infect plants with its own DNA. It does this through horizontal gene transfer. A. tumefaciens is a gram negative bacteria. In the absence of genetic engineering, this bacteria uses horizontal gene transfer to introduce tumors into various plants. Plant geneticists have designed plasmids that contain genes on interest that confer desired traits to these plants. Such traits include longer shelf-life, better resistance to environmental stresses, improved nutrition and even improved taste (1). In order to transfect a plant with A. tumefaciens DNA, the tumor-causing genes in the plant's plasmid must be removed (5). After the plasmid has been disarmed (all harmful genes have been removed), genetic engineers clone their desired insert into the plasmid. These plasmids are given an antiobiotic resistance gene so that successful transformants can be selected for. After the transformation, the plants are grown in media that contain the selected anitbiotic (such as Neomyocin phosphotransferase) (3). If the plants grow, then they have the desired plasmid, which conferred resistance to the plant. If no plants are seen, then the transformation did not work. As for how the actual transformation works, there are two main ways. One was is specific for flowers, the other way can be used in a non-flowering plant as well as a plant that produces flowers. The first way to achieve a transformation is that the flower is dipped in a culture of A. tumefaciens that has been transformed with the desired plasmid (1). This method causes the germline cells to be transfected, which means that the traits will be passed along to the next generation via the gametes. The second way to achieve a transformation is to actually incubate the plant's leaf-discs in a plate with the transformed A. tumefaciens ''culture overnight. These leaf-discs can regrow their plants when placed in specific, nutrition-rich media (2). Environmental Stress Resistance In addition to making a wild-type tomato have a longer shelf-life, plant geneticists are also interested in making the tomato better equipped to grow throughout the entire year, rather than just the winter and fall (1). One of the first types of transgenic tomatoes that aimed to combat this issue, was the anti-freeze tomato. A gene from the winter flounder, called Afa3, confers better resistance to frost and other winter conditions (2). This gene was transfected into a tomato. While the protein worked well in the flounder by preventing ice crystallization in the flounder's blood, it had no effects within the tomato. Two other environmental stresses that were transfected against were high salinity within the environment and drought resistance. Both genes were cloned from rice plants and transfected into the tomato. The protein conferring decreased salinity had no effect on the actual tomato, only on the plant's leaves and roots. The drought resistance gene was expressed in the tomato and showed promise, but the research was eventually discontinued by the FDA (2). The Tomato Vaccine Geneticists are trying to use fruits and vegetables as vectors for vaccines (6). These plants are transfected/infected with genes that will express proteins that will stimulate antibody production within the humans that consume them. Bananas and tomatoes are on the front-line of this new vaccine vector research. This research is currently in the small mammal stage (mice), and will be a few years before human trials are conducted. Vaccines are being tested for many viruses, such as HIV, hepatitis, Anthrax, and even Alzheimer's Disease (4,6). References 1. ''"Agrobacterium-mediated transformation of tomato with rolB gene results in enhancement of fruit quality and foliar resistance against fungal pathogens." ''PMID - 24817272 2. "''Genetically-modified tomato" Wikipedia 3. "The Transgenic Tomato" IA State 4. "''Transgenic tomatoes expressing human beta-amyloid for use as a vaccine against Alzheimer's Disease" ''PMID - PMC2522325 5. "''Agrobacerium tumefaciens" '' Wikipedia 6. ''Vaccines of the Future. ''Organic Gardening. Image 1: Image 2: